audio error in yahoo messenger: plz help

i use xp microsoft and my yahoo messenger shows me this audio error
message when i want to use audio chat" yor are not authorized to jion
this conference".it happaned to me before and i used another account on
my pc and the audio worked.I use net2phone to call:and i did the
following but nothing happened:
1- i used diffenet ID.
2-i used audio wizard oh the messenger.
3-i dont use a proxy.
4-i checked my pc audio setup.
5- i tried to use old version of yahoo.
what i discovered that lots of people have the same problem but no can
solve it even by yahoo help people.Can some one help?